The invention relates to an impact device for generating a stress pulse in a tool, the impact device comprising a frame to which the tool is connectible, and between the frame and the tool a transmission member, such as a transmission piston, the tool being in contact with the tool-side end of the transmission member either directly or indirectly at least part of the time during the generation of the stress pulse, means for generating a force between the frame and the transmission member such that the force tends to push the transmission member towards the tool, and a first hydraulic fluid space on the tool-side relative to the transmission member, whereby the transmission member comprises a first pressure surface located on the side of the first hydraulic fluid space towards the tool, means for leading pressurized hydraulic fluid into said first hydraulic fluid space and for enabling sudden flow of the hydraulic fluid out of said first hydraulic fluid space such that said force between the frame and the transmission member causes, either directly or indirectly via the transmission member and when the transmission member is in contact with the tool, a force compressing the tool in its longitudinal direction and, due to the effect thereof, a stress pulse in the tool in its axial direction, and a hydraulic fluid channel for feeding pressurized hydraulic fluid into the impact device, and a discharge channel for leading the hydraulic fluid out of the impact device.
The invention further relates to a control valve for controlling the work cycle of a hydraulic fluid-driven impact device, a feed channel leading to the impact device and, correspondingly, a discharge channel for leading hydraulic fluid into and out of the impact device, the control valve being intended to be installed rotatingly in a space in a frame of the impact device, at least one hydraulic fluid discharge channel leading to said space, the control valve comprising at least one channel or opening for controlling the flow of hydraulic fluid.
In known impact devices, impacts are achieved by using a reciprocating percussion piston, whose movement is typically achieved hydraulically or pneumatically or in some cases also electrically or by the use of a combustion engine as the power source. A stress pulse is generated in the tool when the percussion piston impacts on the end of the tool or a shank connected thereto.
The impact mechanism of the impact device can also be implemented by using a special stress element to generate an impact pulse. Such a stress element may be a mechanical one-element or multi-element piece subjected to stress in the longitudinal direction of the tool, or hydraulic fluid, arranged in a pressurized state in some space. In these solutions, the stress element is subjected to stress or pressure, respectively, and, at the same time, directly or indirectly pushed against the end of the tool or a shank connected thereto. Hereinafter, in the present patent application and in the claim, the definition ‘stress element’ refers to both a mechanic solution and a solution implemented with hydraulic fluid. Correspondingly, the definition ‘subjected to stress’ refers to both subjecting a mechanical piece to mechanical stress and to subjecting hydraulic fluid to pressure. When these are suddenly released from stress or, correspondingly, the pressure is suddenly allowed to drop, the result is the generation of a stress pulse that is transferred to the tool and that way, through the tool, to the material to be broken. In order for a sufficiently strong stress pulse to be generated, the release of the stress element from stress or pressure has to occur rapidly. On the other hand, the stress has to be achieved in a manner enabling high stresses and high pressures without any limits set by mechanical wear or material load. Consequently, in practice, the stress phase or the pressure of the stress element is raised simplest by the use of a hydraulic medium or hydraulic medium-driven piston and valve structures. To ensure a sufficiently high hydraulic fluid flow in the impact phase at a sufficient speed to achieve the required fast pressure release, the control valve controlling the impacts has to be able to control sufficiently large liquid flows at a sufficiently high frequency.